The present invention relates to voice communication systems, and more particularly to a technique for detecting characteristics of a received signal in the frequency or transform domain to detect received voice signals.
Present voice detection (squelch) techniques use one of the following approaches:
1. "Zero crossing" of the received signal in the time domain are counted to determine the mean frequency, and compare the mean frequency against 1 KHz to determine the existence of voice. This technique does not take advantage of the entire audio spectrum and has a high false alarm rate. PA1 2. The cross-correlation of voice signal with tone is calculated to determine pitch period. This technique is corrupted heavily by noise and is also time-consuming. PA1 3. An out-of-band CW tone used to allow the receiver to detect transmission. A disadvantage of this technique is that energy is spent on the CW tone, thus reducing the amount of power available for voice transmission. In addition, this technique requires the transmitter to send the CW tone and therefore it cannot be implemented in existing radios without circuit modification.